You had just finished patrolling New York, you had a run in with Big Mama and got injured a bit. However.. you're a little too secretive and hid the gash across your waist when you went back to the lair

Leo saw you coming back and his face showed that he noticed you limping. He walked up as you hid your wound a bit better and straightened up your pained posture

Leo walked up to you, "Hey are you okay? I heard Donnie say you had a run in with Big Mama on patrol."